This technical memorandum (TM) is the third in a series concerned
with the feasibility of developing selected surface water sources to
help meet municipal water supply needs within the St. Johns River
Water Management District. The first surface water supply TM
addressed data availability and development of the methodology to be
used in the feasibility evaluation. The second TM addressed selection
of six candidate surface water withdrawal sites for quantitative
analysis. This TM presents the results of the quantitative water supply
availability and yield analysis.
The six candidate withdrawal sites include Lake Griffin on Haines
Creek, located in Lake County, and five sites located on the main stem
of the St. Johns River extending from Cocoa downstream to
Jacksonville. For each of the six candidate withdrawal sites, a similar
series of analyses was conducted.

WATER SUPPLY YIELD
The estimated maximum reliable municipal water supply yield for
each of the six candidate withdrawal sites is summarized below:
Lake Griffin (Haines Creek) 28 mgd
St. Johns River near Cocoa 108 mgd
St. Johns River near Titusville 143 mgd
St. Johns River at Sanford (Lake Monroe) 279 mgd
St. Johns River near De Land 351 mgd
St. Johns River above Jacksonville 419 mgd
The maximum water supply yield estimates are based on application
of the previously established surface water evaluation methodology.
However, because planned SJRWMD minimum flows and levels
analysis for Lake Griffin may result in different, and possibly more
restrictive, withdrawal criteria, only 50 percent of the calculated
maximum yield, or 14 mgd, will be considered in subsequent areawide
alternative water supply evaluations.
Maximum reliable yields for the Lake Griffin and St. Johns River sites
are independent as they are relatively independent hydrologic
systems. Thus, water supply development on Lake Griffin will not
affect the potential for water supply development on the St. Johns
River.

Surface Water: Availability and Yield Analysis

Executive Summary

However, the maximum yield values for the individual St. Johns River
sites are not independent. These values represent the cumulative
amount for each individual site and all upstream sites. For example, if
a 100-mgd reliable water supply were developed near Titusville, then
the maximum reliable yield at De Land (or another downstream site)
would be reduced by 100 mgd.

TREATMENT REQUIREMENTS

Facilities required to develop the surface water sources include a river
diversion structure, an off-line raw water reservoir, a water treatment
plant, and an aquifer storage recovery system. Treatment
requirements vary considerably by location. For example, the Lake
Griffin site is the only true freshwater site, while the St. Johns River
sites will require some desalting facilities, likely reverse osmosis
membrane treatment, to provide the required product water quality.
The four upstream St. Johns River sites provide raw water that can be
classified as either slightly or moderately brackish under certain flow
conditions. The most downstream site, the St. Johns River above
Jacksonville, is tidal and has poor water quality characteristics. Raw
water at this site is classified as saline, which would require extensive
desalting facilities and would generate large quantities of waste
concentrate.
In conclusion, five of the six candidate water supply withdrawal sites
are technically viable municipal water supply sources and should be
considered in subsequent phases of the alternative water supply
investigations. The viable sites include Lake Griffin and the four
upstream sites located on the main stem of the St. Johns River, from
near Cocoa to near De Land. The most downstream site, the St. Johns
River above Jacksonville, does not provide a viable municipal water
supply source and should not be considered further.

STREAMFLOW DURATION ANALYSIS.............................................................................. 16
FLOW DURATION CURVES AND MINIMUM STREAMFLOW REQUIREMENTS................................ 16
Haines Creek.....................................................................................................................................................16
St. Johns River near Cocoa ..............................................................................................................................18
St. Johns River near Titusville....................................................................................................................18
St. Johns River at Sanford ..........................................................................................................................18
St. Johns River near De Land ............................................................................................................. .............21
St. Johns River above Jacksonville ........................................................................................................... 21
EFFECT OF WATER SUPPLY WITHDRAWAL ON FLOW DURATION RELATIONSHIPS ..................25

1 Facilities Required to Develop Reliable Surface Water Supply
to M eet Urban Dem ands ............................................. .............. 7
2 Location of the Candidate Surface Water Withdrawal Sites
in Lake County ................................................. ........................ 13
3 Locations of Candidate Surface Water Withdrawal Sites
on the Main Stem of the St. Johns River...................................... 14
4 Flow Duration Curve for Haines Creek near Lisbon, Florida... 17
5 Flow Duration Curve for the St. Johns River near Cocoa,
Florida ............................................................................................. 19
6 Flow Duration Curve for the St. Johns River near Titusville
(Christm as), Florida .................................................. ........ .... 20
7 Approximate Flow Duration Curve for the St. Johns River
near Sanford, Florida ................................................ ....... ..... 22
8 Flow Duration Curve for the St. Johns River near De Land,
Florida.......................................................... .............................. 23
9 Flow Duration Curve for the St. Johns River above
Jacksonville, Florida ................................................. ........... ..... 24
10 Maximum Effect of Water Supply Withdrawal on Flow
Duration Curve for Haines Creek at Lisbon, Florida.................. 26
11 Maximum Effect of Water Supply Withdrawal on Flow
Duration Curve for the St. Johns River near Cocoa, Florida ..... 27
12 Maximum Effect of Water Supply Withdrawal on Flow
Duration Curve for the St. Johns River near Titusville
(Christm as), Florida .................................................. ........ .... 28
13 Maximum Effect of Water Supply Withdrawal on Flow Duration
Curve for the St. Johns River at Sanford, Florida .................... 29
14 Maximum Effect of Water Supply Withdrawal on Flow Duration
Curve for the St. Johns River at De Land, Florida................... 30
15 Maximum Effect of Water Supply Withdrawal on Flow
Duration Curve for the St. Johns River above Jacksonville,
Florida............................................................ ............................ 31

20 Potential Yield Curve for the St. Johns River near
De Land, Florida....................................... ................ ............... 39
21 Potential Yield Curve for the St. Johns River above
Jacksonville, Florida................................................. ........... ..... 40
22 Surface Water Facility Requirements for Lake Griffin
(Haines Creek) .............................................. ........................ 54
23 Surface Water Facility Requirements for the St. Johns River
near Cocoa...................................................... ........................... 55
24 Surface Water Facility Requirements for the St. Johns River
near Titusville ................................................... ........................ 56
25 Surface Water Facility Requirements for the St. Johns River
at Sanford ......................................................................................... 57
26 Surface Water Facility Requirements for the St. Johns River
near De Land........................................ .................................... 58
27 Surface Water Facility Requirements for the St. Johns River
above Jacksonville ................................... .............................. 59

This technical memorandum (TM) is the third in a series concerned
with the feasibility of developing selected surface water sources to
help meet municipal water supply needs within the St. Johns River
Water Management District (SJRWMD). The first surface water supply
TM addressed data availability and development of the methodology
to be used in the feasibility evaluation (CH2M HILL, 1996a). The
second TM addressed selection of six candidate surface water
withdrawal sites for quantitative evaluation (CH2M HILL, 1996b).
This TM presents the results of the quantitative evaluation of the six
previously selected candidate withdrawal sites using the established
evaluation procedure.
The six candidate withdrawal sites include Lake Griffin on Haines
Creek, located in Lake County, and five sites located on the main stem
of the St. Johns River extending from Cocoa downstream to
Jacksonville. For each of the six candidate withdrawal sites, the
following series of analyses was performed:
Development of flow duration curves
Determination of minimum streamflow requirements and the
maximum water supply withdrawal rate
Evaluation of the effect of water supply withdrawal on the flow
duration relationship
Evaluation of the potential water supply yield as a function of
maximum installed withdrawal capacity
Determination of streamflow water quality characteristics and
water treatment requirements
Estimation of the type and size of water supply facilities required
as a function of the total reliable water supply yield developed
The analysis is primarily based on available streamflow and water
quality records. First, flow duration curves for each site were
developed. Then, minimum streamflow requirements and the
maximum withdrawal rate were determined for each site according to
flow duration curve characteristics. Once these parameters were
determined, the maximum effect of water supply withdrawal on the
existing streamflow duration was determined and reported for each
candidate withdrawal site.

Surface Water: Availability and Yield Analysis

Introduction

The remainder of the feasibility analysis focused on determining
surface water supply facilities requirements. The first step in this
process was developing the potential yield curve for each candidate
withdrawal site. The potential yield is defined as the water supply
yield that could be developed if adequate storage and treatment
facilities are provided and no waste is produced by the treatment
process. This curve defines the relationship between the installed
streamflow diversion capacity and the long-term average flow rate
that can be diverted for water supply purposes. Also, this curve
establishes the maximum water supply that could be developed as a
function of the maximum streamflow diversion rate.
Once the potential yield curve was developed, trial water supply
facilities were selected. Long-term water supply systems were then
simulated to evaluate the reliability of the trial water supply systems
to meet a variety of target yields. By doing so, the facilities required to
meet a projected long-term demand at the desired reliability were
established.
Preliminary water treatment process requirements were determined
from the water quality characteristics observed at each candidate
withdrawal site. Once conceptual treatment requirements were
established, the net reliable yield for each trial water supply facility
was estimated. The final results are relationships between net reliable
water supply yield and facility requirements for each candidate
withdrawal site.
This TM concludes with a proposed procedure for developing
planning-level cost estimates for the required surface water supply
facilities. Planning-level water supply facility cost estimates and
planning-level cost functions will be the subject of the fourth and final
surface water supply TM. These cost estimates will then be available
for use in the University of Florida Decision Model, which will
compare the surface water supply alternative with other water supply
strategies.

Surface Water: Availability and Yield Analysis

Methods

METHODS

The methods applied to the surface water supply availability and yield
analysis are fully documented in TM B.l.f, Surface Water Data
Acquisition and Evaluation Methodology (CH2M HILL, 1996a). This
section presents a summary of the methodology established in that
TM.

FACTORS AFFECTING SURFACE WATER SUPPLY
DEVELOPMENT
Several factors affect the technical feasibility of developing a surface
water supply source, such as streamflow characteristics, minimum
streamflow requirements, water supply demand characteristics, and
required system reliability.
Streamflow Characteristics
Important streamflow characteristics include streamflow magnitude,
streamflow variability, and water quality. The magnitude of the
streamflow, which is defined as the long-term average discharge rate
or watershed yield, establishes the total water resource available. In
general, the larger the streamflow magnitude, the greater the potential
for significant water supply development.
Streamflow variability defines the day-to-day, month-to-month, and
year-to-year variation of the total streamflow. Variability can be as
important as magnitude in determining the economic feasibility of
developing a surface water supply source. This is because a highly
variable source is more difficult to develop than a source with little
variability. In general, variable sources require larger storage facilities
and are therefore more expensive to develop than sources with less
variable streamflow regimes.
The streamflow characteristics of magnitude and variability are
defined by observed streamflow records. Fortunately for this analysis,
long-term streamflow records are available at, or near, each of the six
candidate withdrawal sites. Daily streamflow records are used to
develop flow duration curves, which illustrate the inherent variability
of the source.
The long-term monthly streamflow array for each candidate
withdrawal site is used directly in the system simulation analysis.

Surface Water: Availability and Yield Analysis

Methods

Therefore, streamflow magnitude and variability are explicitly
accounted for throughout this surface water supply feasibility analysis.
Water quality records are used to define the characteristics of the raw
water available for treatment. These data are used to establish the
appropriate treatment processes required to deliver high-quality
product water. Treatment requirements greatly influence the cost of
developing each individual candidate water supply site. For example,
if desalting is required, treatment facilities will be relatively more
expensive and the reliable yield will be reduced because part of the
diverted flow will become waste concentrate.
Useful water quality data were available at or near each of the six
candidate withdrawal sites.
Minimum Streamflow Requirements
Minimum streamflow requirements for streams and rivers within
SJRWMD will be defined, in the future, by the ongoing minimum
flows and levels program. However, at this time, minimum flows and
levels have not been established for any of the water bodies or
withdrawal sites considered in this evaluation. Thus, approximate
minimum streamflow requirements were established for this
preliminary evaluation of surface water supply feasibility. Once
minimum flows and levels are established for the candidate
withdrawal sites considered in this TM, the feasibility of developing a
viable surface water supply should be re-evaluated using the site-
specific minimum flows and levels criteria established by SJRWMD.
For this effort, minimum streamflow requirements are defined as the
positive streamflow rate observed 95 percent of the time. This means
that at least 5 percent of the time (during low-flow periods) water
supply withdrawal will not be allowed. In addition, the maximum
withdrawal rate considered is equal to 25 percent of the long- term
average flow rate. Lesser withdrawal rates are also considered.
Consider, for example, a stream with positive flow 97 percent of the
time and a mean flow rate of 500 cubic feet per second (cfs). The
allowable diversion frequency would be 92.2 percent of the time
(0.95 x 0.97 = 0.922), and the maximum diversion rate would be 125 cfs
(0.25 x 500 = 125).

Surface Water: Availability and Yield Analysis

Methods

Demand Characteristics
The characteristics of the projected demand to be met by the water
supply system also influences the water supply facilities required to
meet the demand. For this effort, only municipal demands are
considered. Demand characteristics of interest include the long-term
average demand to be met, or average daily demand (ADD), the
maximum daily demand to be met (MDD), and the seasonal
distribution of demands. The seasonal distribution of demands is
defined by the ratio of monthly demands to the ADD.
In this feasibility analysis, the targeted yields are varied over a range
compatible with the expected water supply yield for a given candidate
withdrawal site. The objective is to define facilities requirements as a
function of demand met. The monthly demand ratios previously
established for this analysis are based on the City of Cocoa operational
experience reported below:
Month Demand Ratio
Jan 0.868
Feb 0.919
Mar 1.059
Apr 1.127
May 1.149
Jun 1.070
Jul 1.084
Aug 1.067
Sep 1.002
Oct 0.944
Nov 0.892
Dec 0.879
In addition, the MDD is assumed to be equal to 1.5*ADD.
Required System Reliability
Domestic water supply systems must be highly reliable, in that they
must be able to supply the desired quantity and quality of water for a
high percentage of the time. In most cases, however, an inability to
meet the desired target yield, or target yield deficiency, means
providing only a portion of the desired yield or providing water that
does not fully meet all desired quality criteria. When a yield
deficiency occurs, implementation of water use restrictions is more
likely to occur than a complete lack of supply.

Surface Water: Availability and Yield Analysis

Methods

For the purpose of this preliminary feasibility analysis, the previously
established water supply system reliability target is 98.3 percent. This
value is based on the allowance of an average of one monthly target
yield deficiency once every 5 years.

GENERAL FACILITIES REQUIREMENTS
The facilities required to develop a safe, reliable surface water supply
include some combination of the following components (Figure 1):
River diversion structure
Raw water storage
Water treatment plant
Aquifer storage recovery (ASR)
Under favorable conditions, including a high-volume, low-variability
source and limited water supply needs, the required water supply
system may be developed with only a river diversion structure and a
water treatment plant. However, in most situations, some type of
storage will be required to provide the system reliability.
Raw water will likely be available for diversion, in quantities adequate
to meet the desired yield, for only a portion of the time. Storage
facilities, including either raw water storage reservoirs or ASR
systems, can be used to store water when it is available for later use
when it is needed. Storage provides the flow attenuation necessary to
match a variable water supply source to a variable water supply
demand.
River Diversion Structure
A river diversion structure consists of a raw water intake and a
pumping station. In most cases, some type of coarse screen or bar
screen is provided to prevent damage to the pumps or other
downstream treatment equipment. The diversion pumping station
capacity (Qd) must be sized to allow diversion of the necessary volume
of water, which is subject to withdrawal constraints defined by
minimum streamflow requirements and maximum allowable
diversion rates.
Raw Water Storage Reservoir
There are two types of raw water storage reservoirs: on-stream
reservoirs and off-line reservoirs. Development of on-stream
reservoirs requires construction of a dam across the stream, flooding a

Surface Water: Availability and Yield Analysis

Raw Water Diversion and
Pumping Station

Finished Water
ASR System

Off-Line Raw
Water Storage
Reservoir

Methods

portion of the upstream valley and subsequently providing the
required water supply storage. Off-line reservoirs, which are
constructed adjacent to the free-flowing stream, are filled by pumping
divertable streamflow into the reservoir. The off-line reservoir is
usually built by constructing a levee around the perimeter of the
reservoir site. The storage volume provided is then a function of the
area enclosed and the depth to which water can be impounded.
Both on-stream and off-line reservoirs receive additional inflow from
direct rainfall and incur water losses through lake evaporation. Under
certain conditions, additional water could also be lost by seepage.
In Florida, construction of on-line reservoirs is difficult because stream
valleys are wide and favorable dam sites are rare. In addition, the
construction of on-line reservoirs greatly impacts the natural flow
regime of a stream, often flooding productive adjacent wetlands. In
contrast, off-line reservoirs do not interfere with the natural
streamflow regime and, therefore, are less environmentally disruptive
than on-line reservoirs. However, off-line reservoirs are usually
located on or near floodplains, where they may impact wetlands.
For this preliminary feasibility analysis, only off-line reservoirs will be
considered and their use will be minimized. Priority will be given to
using ASR as the primary storage method; however, off-line raw water
storage will be used to provide a buffer between the river diversion
structure and the water treatment plant, providing some flexibility in
operation. The presence of a raw water storage reservoir will allow
the plant to operate during short periods when streamflow diversion is
not allowed because of minimum streamflow requirements.
A minimum off-line raw water storage reservoir that provides 5 days
of operational storage is included in this analysis.
Water Treatment Plant
The purpose of the water treatment plant is to provide a safe, potable
finish water that meets all necessary drinking water standards. If the
raw water is of reasonably high quality, then conventional treatment is
usually all that is necessary. For surface water sources, conventional
treatment usually consists of some type of clarification and filtration
with disinfection. If the raw water is of poor quality, including a high
dissolved minerals content, membrane treatment may also be required,
which produces a waste concentrate. Therefore, addition of membrane

Surface Water: Availability and Yield Analysis

Methods

treatment would result in reduction of the net water supply yield, as
well as additional requirements for a concentrate disposal system.
The quality characteristics of the raw water define treatment
requirements and, in part, treatment costs. However, the demands to
be met and the amount and type of storage provided will define the
treatment capacity (Qt) requirements. If no finish water storage is
provided, by an ASR system for example, then the treatment plant
must be sized to meet the maximum day demands (Qt = MDD). Or, if
finish water storage is provided, the treatment plant can be somewhat
smaller because maximum day demands can be met from finish water
storage.
ASR Systems
In general, ASR systems can be used to store both raw water and
treated finish water (Pyne, 1995). In raw water applications, the ASR
system could replace the off-line raw water storage reservoir discussed
previously. However, in most water supply applications implemented
to date, ASR has been used to provide treated water storage, so only
treated water ASR is being considered for SJRWMD. Water processed
by the water treatment plant and not needed at the time of treatment is
injected into a suitable storage aquifer for later recovery and
distribution. In general, the recovered water is re-disinfected, but no
additional treatment is required.
ASR involves injecting water to be stored into a suitable aquifer. The
native ground water is displaced by the injected water, which is then
available for recovery when needed. However, some inefficiencies and
losses occur, which prevent all of the water injected from ultimately
being recovered and used. As water is injected, some of it mixes with
the native ground water. Depending on the mixing characteristics of
the aquifer and the quality of both the injected water and native
ground water, only a portion of this mixture can be recovered before
the water quality is unacceptable for the intended purpose.
The mixing characteristics of the storage aquifer and water quality of
the native ground water are not usually as restrictive in ASR
applications as they might first appear, if the ASR system is developed
and operated properly. Even if the native ground water quality is
poor and considerable initial mixing occurs, a viable ASR system can
still usually be developed by injecting an initial volume of treated
water to develop a buffer between the native ground water and treated
injected water. Once developed, the buffer will allow good recovery

Surface Water: Availability and Yield Analysis

Methods

efficiencies if the injected water is not recovered, but is allowed to
remain in the buffer.

SIMULATION OF CONTINUOUS WATER SUPPLY SYSTEMS
Direct calculation of requirements for surface water supply facilities
for a given set of conditions is not possible because of the complexity
of the system and the large number of interacting factors. Facility
requirements must be determined on a trial-and-error basis using a
structured, continuous simulation approach.
Overview and Application
The water supply systems simulation was designed to simulate the
long-term operation of a trial water supply system subject to a given
set of monthly demands and to track the performance of the system, as
measured in terms of its reliability or ability to meet demands. The
basic approach that was used defines a number of trial water supply
systems using appropriate components, as defined in Figure 1. Several
sets of monthly target yield arrays (small-to-large) were also
established.
Each trial water supply system was then evaluated by the simulation
relative to its ability to deliver the desired yields. The reliability of the
trial system is tracked for each target yield array simulated. In this
manner, relationships between facility size and water supply yield for
the given system reliability, were developed. This is the basic
approach used previously by CH2M HILL to evaluate surface water
supply facilities requirements for the Peace River Water Supply
System (CH2M HILL, 1985, 1987, 1993; Wycoff, 1985) and for the
Florida Lower East Coast water supply planning project
(CH2M HILL, 1994).
The procedure involves multiple, long-term simulations. In a given
application, for each candidate withdrawal site, six trial water supply
systems were identified and ten target yield arrays were defined. Sixty
simulation runs were used to fully define facility requirements, yield,
and reliability relationship. Some applications involved more than one
complete iteration because the initially defined target yield levels
proved to be inappropriate once initial results from the simulation
were available.
The simulation uses a monthly time step, which is the appropriate
level of detail for preliminary surface water supply planning purposes

Surface Water: Availability and Yield Analysis

Methods

(McMahon, 1992). The length of simulation varied, depending on the
streamflow records used. In general, whole calendar years of monthly
streamflow records were used.
Simulation Logic
The simulation was constructed around a flow distribution logic that
defines how the water supply system will operate and provides
criteria defining how a given monthly demand will be met, based on
the monthly divertable streamflow, available facilities, and previously
stored water. The flow distribution logic is defined as follows:
Condition A. Monthly divertable river flow is greater than or equal
to monthly target yield
Treat diverted flow and distribute to meet desired yield.
Treat and inject into the ASR system remaining divertable flow
up to the available treatment capacity or ASR injection capacity,
whichever is less.
Remaining divertable flow, if any, goes to the surface reservoir.
If the surface reservoir is full, potential divertable flow is lost
from the water supply system (i.e., not diverted).
Condition B. Monthly divertable flow is less than monthly target
yield
Treat divertable flow, if any, and distribute.
Obtain remaining desired yield from the ASR system up to the
maximum recovery rate or recoverable ASR volume, or both.
Obtain remaining desired yield, if any, from the surface
reservoir, treat, and distribute.
If total desired yield cannot be met, a yield deficit occurs.
The above logic is applied to each time step in the simulation and the
number of yield deficits is tracked. The total number of deficits
divided by the total number of simulation time steps is equal to the
water supply system deficit rate. One minus the deficit rate then
equals system reliability.

Surface Water: Availability and Yield Analysis

Methods

SELECTED CANDIDATE WITHDRAWAL SITES
Initially, many sites were considered on the St. Johns River and the
Haines Creek/Palatlakaha Chain of Lakes. The site selection process
considered location of streamflow gauging stations, municipal water
supply demand growth areas, and potential maximum surface water
supply availability. Based on these criteria, the six candidate sites
were chosen for this analysis.
Only one site from the Haines Creek/Palatlakaha Chain of Lakes
watershed was selected. The chosen site is Lake Griffin in Lake
County (Figure 2), which could potentially supply a portion of the
future projected needs of northern Lake County. Lake Griffin receives
the majority of its inflow from Haines Creek, and the water availability
analysis is based on the Haines Creek gauging station, located near
Lisbon Florida (U.S. Geologic Survey [USGS] Gauge No. 2238000). For
the purpose of this feasibility analysis, withdrawals from Lake Griffin
will only be allowed when Haines Creek flow rates are above the
minimum streamflow requirements established for the Haines Creek
gauge.
The following remaining five candidate withdrawal sites are all
located on the main stem of the St. Johns River, as shown in Figure 3:
St. Johns River near Cocoa
St. Johns River near Titusville
St. Johns River at Sanford(Lake Monroe)
St. Johns River near De Land
St. Johns River above Jacksonville
USGS stream gauging records, including daily flow observations and
periodic water quality data, are available at or near each of these sites.
Streamflow and water quality characteristics for the Cocoa site are
defined by USGS Station No. 2232400, located near Cocoa. The
gauging station near Christmas Florida (2232500) is used for the
Titusville site evaluation.
Data from the USGS De Land gauging station (2236000) are used to
establish streamflow characteristics for both the De Land site and the
Sanford site. For the Sanford site, which is located upstream from the
De Land gauge, the observed streamflow values are multiplied by the
previously established adjustment factor of 0.797 to account for the
reduced streamflow expected at the upstream location (CH2M HILL,
1996b).

Surface Water: Availability and Yield Analysis

M A R10 N COUN T Y

Lady Lake La k
I "3 Lhe Umatill

SLi\bon

LA r LOI 2.96 mgd

O Mt. Dora
S1.64 mgd

POLK COUNTY

Figure 2. Location of the Candidate stream gauging site
Surface Water Withdrawal Site in 122-365- Gauging station
Lake County. 3. number/approximate maximum
SC mg developable surface water supply Approximate
Approximate
7.93 mgd Projected public water supply Scale in Miles
S Withdrawal site
A Withdrawal site 0 5 10

I ORANGE 223250
S73.95 mgd 166m
| 2232400
*-*----- 127 md-
I

OSCE OLA

'I23

-p

iourne

Figure 3. Locations of Candidate Stream gauging site
Surface Water Withdrawal Sites on theauin station
Main Stem of the St. Johns River. 2244450 au pproxmate maximum
768 mad developable surface water supply Approximate
Approximate
73.95 mgd Projected public water supply Scale in Miles
S Withdncrease 0 10
A Withdrawal site 0 10 20

Methods

The final St. Johns River candidate withdrawal site is located in
northern St. Johns County, just upstream of the City of Jacksonville.
Streamflow and water quality records from the USGS station near
Switzerland (2246500) are used to establish the characteristics of this
site.

Surface Water: Availability and Yield Analysis

Streamflow Duration Analysis

STREAMFLOW DURATION ANALYSIS

The streamflow duration analysis includes three major parts. First,
individual flow duration curves were developed for each candidate
withdrawal site. These curves, which are based on analysis of long-
term USGS daily flow records, define streamflow magnitude and
variability.
The previously developed minimum streamflow criteria were then
applied to the flow duration curves to establish approximate minimum
streamflow requirements and the maximum streamflow diversion rate
considered in this feasibility analysis. Once these parameters were
established, the effect of water supply withdrawal on each streamflow
duration relationship was evaluated.

FLOW DURATION CURVES AND MINIMUM
STREAMFLOW REQUIREMENTS
Haines Creek
Figure 4 presents the flow duration curve for Haines Creek near
Lisbon Florida. During the 52-year period of record, Haines Creek
flow has range from no flow to a daily maximum of 1,470 cubic feet
per second (cfs), with a mean of 248 cfs. Periods of no streamflow are
rare, occurring only about 0.7 percent of the time, or 2 to 3 days per
year on the average.
Based on previously established minimum flow criteria, the minimum
streamflow requirement for Haines Creek is 14 cfs. This flow rate is
exceeded 94.3 percent of the time (0.95 0.993 = 0.943), which is also
the maximum allowable diversion frequency. Again, using the
previously established criteria, the maximum diversion rate
considered in this analysis is 62 cfs (40 mgd), which is equal to
25 percent of the long- term observed mean flow rate.
SJRWMD plans to conduct a minimum flows and levels analysis for
Lake Griffin. Once this analysis is complete, it is likely that a site-
specific surface water diversion rule for Lake Griffin, based on lake
stage, will be established. It is also likely that this rule will differ from
the Haines Creek criteria used in this preliminary water supply
feasibility analysis.

Because of the uncertainty associated with the outcome of the planned
minimum flows and levels analysis for Lake Griffin, it is possible that
the estimated maximum water supply yield resulting from this
preliminary water supply evaluation could be overstated. For this
reason, an additional constraint could be placed on the Lake Griffin
candidate withdrawal site when evaluated by the University of Florida
decision model. The additional constraint would limit the maximum
water supply considered to 50 percent of the theoretical maximum
obtained by application of the streamflow diversion criteria
established for this investigation.
The feasibility of developing a viable water supply from Lake Griffin
should be re-evaluated once the planned Lake Griffin minimum flows
and levels analysis is complete.
St. Johns River near Cocoa
Figure 5 presents the flow duration curve for the St. Johns River near
Cocoa. Streamflow has ranged from 5.6 cfs to 10,700 cfs at this station.
The long-term mean flow is 958 cfs. The maximum diversion
frequency, based on these streamflow characteristics, is 95 percent.
This flow frequency corresponds to a minimum streamflow
requirement of 57 cfs, as determined from the flow frequency curve.
Therefore, for the purpose of this analysis, water supply diversions
will not be allowed when streamflow is less than 57 cfs and the
maximum diversion rate to be considered is 239 cfs (154 mgd).
St. Johns River near Titusville
The overall streamflow characteristics of the St. Johns River near
Titusville, as illustrated in Figure 6, are similar to the characteristics
near Cocoa. However, during the 61-year period of record, there were
5 days with no streamflow. The mean flow is 1,273 cfs and the
maximum observed daily flow rate is 11,600 cfs. Based on our
planning criteria, the minimum streamflow requirement is 70 cfs and
flow can be withdrawn for water supply 95 percent of the time. The
maximum diversion rate investigated is 318 cfs (206 mgd).
St. Johns River at Sanford
The flow duration curve for the Sanford (Lake Monroe) candidate
withdrawal site is based on analysis of the flow records from the
De Land gauge adjusted for the smaller tributary area. As previously
discussed, the De Land gauging station daily flow data were

Figure 6. Flow Duration Curve for the St. Johns River near Titusville (Christmas), Florida.

Streamflow Duration Analysis

multiplied by an adjustment factor equal to 0.797. The characteristics
of these adjusted data are illustrated in Figure 7.
As Figure 7 shows, the estimated streamflow characteristics for the
Sanford site are somewhat different than those observed at the two
previous upstream sites. At the Sanford site, significant negative or
upstream flows are exhibited. Daily flow rates range from -2,966 cfs to
13,629 cfs, and the mean flow rate is 2,425 cfs. Although significant
negative flow rates can occur, they only occur about 2.3 percent of the
time.
Applying our planning criteria, the maximum diversion frequency for
the Sanford site will be about 92.8 percent of the time and the
corresponding minimum streamflow requirement is 571 cfs. The
maximum stream diversion rate to be considered is 606 cfs (392 mgd).
St. Johns River near De Land
Figure 8 presents the flow duration curve for the De Land candidate
withdrawal site. Since both the De Land and Sanford flow duration
curves were derived from the same observed streamflow sequence, the
shapes of these curves are the same. However, the magnitude of flow
at De Land is larger than that at Sanford.
Daily flow rates range from -3, 030 cfs to 17,100 cfs and the mean flow
rate is 3,043 cfs. Applying the streamflow diversion criteria for this
investigation, the maximum diversion frequency for the De Land site
will be about 92.8 percent of the time and the corresponding minimum
streamflow requirement is 717 cfs. The maximum stream diversion
rate to be considered is 761 cfs (492 mgd).
St. Johns River above Jacksonville
The final withdrawal site considered is the St. Johns River in northern
St. Johns County, just upstream from Jacksonville. As can be seen in
Figure 9, the streamflow variability at this site is large. Daily flow
rates range from -202,000 cfs to 185,000 cfs, and negative or upstream
flow occurs nearly 30 percent of the time. However, the net freshwater
outflow is substantial. The mean flow equals 9,129 cfs.
Applying the streamflow diversion criteria for this investigation, the
minimum streamflow requirement is 1,663 cfs and water supply
withdrawal would be allowed 67.2 percent of the time. The maximum
withdrawal rate considered here is 2,282 cfs (1,475 mgd).

Figure 9. Flow Duration Curve for the St. Johns River above Jacksonville, Florida.

..... -

Streamflow Duration Analysis

The extremely large daily flow range and frequent upstream flow are
caused by strong tidal influences at this downstream location. These
tidal influences would make development of a municipal water supply
difficult because of the large volume and significant duration of
seawater inflow. Because water supply withdrawals can only occur
during a certain time period, the facilities required for water supply
development would be relatively large compared with the amount of
water that would be gained. In addition, the raw water quality will be
extremely variable because of tidal mixing, resulting in difficult and
expensive treatment requirements.
Also, the available streamflow records at this site are of poor quality.
Again, this is because of the tidal influences, which make flow
measurement difficult. Large incoming and outgoing tidal flows occur
daily, and the differences in these flow volumes is the net daily
outflow or river flow.

EFFECT OF WATER SUPPLY WITHDRAWAL ON FLOW
DURATION RELATIONSHIPS
If a significant surface water supply were developed at any of the
candidate withdrawal sites, the streamflow duration relationship
would be modified. An analysis was conducted to quantify the
maximum effects that could result from these withdrawals at each of
the six sites.
In each case, the effect of withdrawal at the maximum rate considered,
as well as withdrawals at 1/3 and 2/3 of the maximum, were
evaluated. Modified flow duration curves, one for each withdrawal
rate, were developed and are shown in Figures 10 through 15. These
figures also demonstrate the effect of withdrawal on the entire
streamflow regime and on the normal to low-flow regime.
The effect of water supply withdrawal using the previously
established withdrawal criteria are similar for each site. In the upper
portions of Figures 10 through 15, the effects relative to the entire
streamflow regime are shown. In most cases, when the entire
streamflow regime is considered, the effects on the flow duration curve
appear to be relatively minor.
However, the effects on the flow duration relationship are more
apparent in the bottom portions of Figures 10 through 15, which
illustrate only the low and moderate flow regime. Under these
conditions, water supply development tends to flatten the flow
duration curve. At flow rates less than the minimum withdrawal rate,

Figure 15. Maximum Effect of Water Supply Withdrawal on Flow Duration Curve for the
St. Johns River above Jacksonville, Florida.

Streamflow Duration Analysis

the flow duration relationship would be unchanged as diversion
would not be allowed. However, the duration of time at or near the
low-flow value may increase noticeably.
This flattening effect appears to be more pronounced for the candidate
withdrawal sites with the smallest total streamflow magnitude; for
example, at the Haines Creek site (Figure 10) and St. Johns River site near
Cocoa (Figure 11). The apparent effect on the Haines Creek flow regime
is only theoretical if the water supply withdrawal is located in Lake
Griffin, as envisioned. The creek itself would not be affected because
the water would actually be withdrawn from the downstream lake.

Surface Water: Availability and Yield Analysis

Potential Yield Analysis

POTENTIAL YIELD ANALYSIS

The purpose of the potential yield analysis is to develop a quantitative
relationship between installed river diversion capacity and the
maximum long-term water supply that could be developed. The
potential yield analysis establishes the maximum theoretical water
supply yield for each diversion capacity investigated. This is a
necessary intermediate step between the flow duration analysis and
determination of water supply facility requirements because it
establishes the upper limit of the developable water supply and
provides insight into the magnitude of the facilities required to
develop each site.
Potential yield is a function of the minimum streamflow criteria, the
maximum installed water supply diversion capacity, and the
streamflow variability. For each withdrawal site, the minimum
streamflow has been determined by applying the established
streamflow diversion criteria, and streamflow variability is defined by
the observed streamflow records. Therefore, the only remaining
variable is the installed diversion capacity. For each diversion capacity
analyzed, the potential yield is calculated for each observed daily
streamflow. These individual daily potential yield values are then
averaged over the period of record to establish the overall potential
yield for that diversion capacity. The process is repeated for a number
of diversion capacities to establish a relationship between installed
diversion capacity and total divertable flow or potential yield.
For example, consider the St. Johns River near Cocoa, which has a
minimum streamflow requirement of 57 cfs (about 37 mgd), with an
installed river diversion capacity of 50 mgd. If the streamflow on a
given day is 30 mgd, which is less than the minimum streamflow
requirement, then the allowed diversion for that day is zero. If,
however, the daily streamflow is equal to 60 mgd, then the allowable
diversion is 23 mgd (60 mgd minus 37 mgd). If the daily streamflow is
large, say 300 mgd, then the withdrawal that day is limited by the
diversion capacity and would be equal to 50 mgd. The divertable
amount of water is calculated on a daily basis for the entire period of
streamflow record to establish the long-term potential yield for each
maximum diversion capacity considered.
The potential yield curve for each candidate withdrawal site is a
function of streamflow magnitude and variability and the minimum
streamflow criteria applied. Potential yield curves are both site-

Surface Water: Availability and Yield Analysis

Potential Yield Analysis

specific and applicable only for a given set of minimum flow criteria.
Thus, the potential yield analysis presented here applies only to the
previously established minimum streamflow requirements. If these
criteria change, then the potential yield curves, subsequent facility
requirements, and water supply development costs will also change.
The potential yield curves for each of the six candidate withdrawal
sites are illustrated in Figures 16 through 21. In each case, the installed
river diversion capacity, in mgd, is plotted on the x-axis and the
potential yield, in mgd, is shown on the y-axis. An empirical equation
was fit to each potential yield curve, and each of these equations is
shown on the figures. The equations may be used to obtain an
estimate of the potential yield for any diversion rate up to the
maximum.
The maximum diversion rate considered and the resulting maximum
potential yield are also shown on Figures 16 through 21. For example,
on Figure 16, which shows the potential yield relationship for Haines
Creek, the maximum diversion rate investigated is 40 mgd and the
resulting maximum potential yield is 30 mgd, or about 75 percent of
the diversion capacity. Because the maximum diversion rate is
25 percent of the mean streamflow, the maximum potential yield in
this case is equal to about 18.8 percent (0.75 x 0.25 = 0.188) of the total
streamflow. Table 1 summarizes the maximum potential yield of each
candidate withdrawal site as a function of the mean annual
streamflow.
Table 1 also provides some insight into the relative water supply
development potential of each candidate withdrawal site. The yield
ratio, which is defined as the potential yield divided by the installed
diversion capacity (PY/Qd), illustrates the relative scale of facilities
required at each site. In general, a site with a larger yield ratio will
require smaller facilities relative to the water supply developed. Based
on a comparison of the yield ratio, the most attractive sites would be
the St. Johns river at Sanford or the St. Johns River near De Land. The
yield ratio at these locations is equal to 84 percent, which represents an
efficient use of constructed water supply facilities.
The least desirable location would be the St. Johns River near
Jacksonville, with a yield ratio of just 64 percent. This low-yield ratio
is a direct result of the significant tidal influences that restrict the time
period during which flow could be withdrawn from the river.
Therefore, facilities at this site would have to be proportionately larger
to meet a given target yield.

Surface Water: Availability and Yield Analysis

35

30

' 25

A
20

15
PY = Qd/(1.058 + 0.00712*Qd)
10

0 5 10 15 20 25 30 35 40 45
Diversion Capacity (Qd) [mgd]

Maximum Diversion Rate = 40 mgd
Maximum Potential Yield = 30 mgd

Figure 16. Potential Yield Curve for Haines Creek at Lisbon, Florida.

140

120

:' 100

80

60 ---

PY = Qd/(1.0555 + 0.00124*Qd)
0
0. 40

20 -

0
0 20 40 60 80 100 120 140 160
Diversion Capacity (Qd) [mgd]

Maximum Diversion Rate = 154 mgd
Maximum Potential Yield = 124 mgd

180

160

140

120

S100

S80

SPY = d/(1.06237 + 0.000868*d)
2 60

40

20
4 0---------------------------

100 150
Diversion Capacity (Qd) [mgd]

200

Maximum Diversion Rate = 206 mgd
Maximum Potential Yield = 166 mgd

-I

350

300

S250

a. 200

150

SPY = Qd/(1.0635 + 0.000312*Qd
D- 100 -

50

0 50 100 150 200 250 300 350 400
Diversion Capacity (Qd) [mgd]

Maximum Diversion Rate = 392 mgd
Maximum Potential Yield = 331 mgd

Figure 19. Potential Yield Curve for St. Johns River at Sanford, Florida.

Facility requirements for each candidate withdrawal site were
determined by simulating the water supply systems and evaluating
the treatment requirements, based on analysis of available water
quality data. The first step in this process is to establish the initial
target yield array and the trial facility components array to be
evaluated. Both of these arrays are based on the potential yield curve
of the withdrawal site.
For example, consider the St. Johns River near Cocoa, with an
estimated maximum potential yield of 124 mgd (Figure 17). As
previously discussed, the maximum reliable yield will probably be
somewhat less than this value. Therefore, the trial average daily yield
investigated was limited to 120 mgd or less. The trial average daily
yield array was established on equal increments of from 12 to 120 mgd.
Initial target yields for each of the six candidate withdrawal site were
selected in a similar manner.

TRIAL FACILITY COMPONENTS
The trial facility components were also selected on the basis of the
potential yield curve and selected interrelationships among the
components. Major surface water supply system facilities, which are
identified in Figure 1, include a raw water diversion structure, a raw
water off-line storage reservoir, a water treatment plant, and a treated
water ASR system.
Raw Water Diversion and Pumping Station
Again, considering the St. Johns River near Cocoa, the maximum
diversion capacity considered is equal to 154 mgd, as illustrated in
Figure 17. The maximum diversion rate was divided into six elements
(ranging from 25.7 mgd to 154 mgd) to define the diversion capacity of
the six trial water supply systems. The sizes of the remaining
components are then based on the diversion capacity to define
reasonably balanced trial water supply systems.
Off-line Raw Water Storage Reservoir
The purpose of the off-line raw water storage reservoir is primarily to
provide operational flexibility. Because streamflow cannot be diverted

Surface Water: Availability and Yield Analysis

Surface Water Supply Facility Requirements

for at least 5 percent of the time, the raw water storage allows the plant
to continue operation while withdrawals are not allowed. Because
shutting down and starting up a water treatment plant is a significant
task, the frequency of shut-down and start-up should be minimized.
For the purpose of this preliminary facilities analysis, the off-line
storage reservoir is sized to provide 5 days of storage, based on the
installed diversion capacity. During periods when streamflow
withdrawals are not allowed, plant operations would probably be
reduced to approximately 20 percent of plant capacity, but would not
be shut down completely. Thus, the off-line reservoir would allow the
plant to operate at this reduced rate for at least 25 days before it would
be necessary to completely cease operations.
An off-line raw water storage reservoir would also provide other
functions and operational flexibility. For example, if a contaminant is
spilled in the river, the raw water intake could be closed while the
contaminated flow moves downstream, without interrupting plant
operations. In addition, the raw water storage reservoir would
provided some sedimentation and mixing of the raw water prior to
entering the treatment facilities.
The off-line storage reservoir may be difficult to site and permit, given
that these reservoirs will probably be located near the river
withdrawal site and, therefore, within or adjacent to floodplains or
wetlands, or both. The need for the off-line reservoir is driven in part
by the assumed minimum streamflow criteria, which would not allow
water supply diversion for at least 5 percent of the time during low
streamflow periods. If the streamflow diversion criteria were relaxed
to allow reduced diversion during low-flow periods (say 20 percent of
treatment capacity), then the need for the off-line reservoir would be
reduced and, possibly, could be eliminated. To a large extent, the
environmental trade-off is whether it is better to allow some reduced
diversion at all times and avoid floodplain or wetland encroachment,
or fully protect the riverine system during low-flow periods. This
trade-off will likely be answered on a case-by-case basis if surface
water supply proves to be a technically and economically feasible
water supply option.
An off-line storage reservoir may not be necessary at the Lake Griffin
site, which is itself a large reservoir. If some water supply withdrawal
were allowed on a continuous basis, it may be possible to develop a
viable water supply without constructing a separate off-line raw water
storage reservoir. The same general reasoning also applies along the

Surface Water: Availability and Yield Analysis

Surface Water Supply Facility Requirements

main stem of the St. Johns River. Because of its mild slopes, the
St. Johns River system is very much like a system of interconnected
lakes. Again, if some continuous diversion were allowed, the off-line
reservoir component may be unnecessary.
The only currently operational municipal surface water supply on the
St. Johns River is located on Lake Washington and serves the City of
Melbourne, Florida. This system does not include an off-line raw
water reservoir. However, the City of Melbourne also uses ground
water as a source of supply. Therefore, the overall reliability of the
water supply system does not depend on surface water alone. A
stand-alone surface water supply system located on the Peace River in
southwest Florida does incorporate an off-line raw water reservoir.
Therefore, examples of each application exist. The final decision for a
given site should be based on detailed engineering alternatives and
environmental systems analysis.
For the purpose of this preliminary feasibility analysis, the off-line raw
water reservoir is included because a reservoir will be necessary to
meet the minimum streamflow criteria established for this
investigation. However, the cost of the off-line reservoirs will be
tracked separately so that alternatives that do not include this
component can be evaluated by SJRWMD if desired.
Water Treatment Plant
The conventional water treatment plant capacity is set equal to
95 percent of the raw water diversion capacity. The small difference
between the diversion capacity and treatment capacity allows some
capability to refill the off-line reservoir, while at the same time
operating the water treatment plant at full capacity.
If desalting is required, it is assumed that RO treatment will be
provided following conventional surface water treatment. The
required RO treatment capacity will vary with each candidate
withdrawal site, depending on water quality characteristics (including
variability) of the raw water. In each case, the RO treatment capacity is
expressed as a percentage of the conventional treatment capacity (from
0 to 100 percent). Where desalting is required, a split-stream treatment
system will be provided because the degree of desalting required
could vary significantly with river flow or other factors. When surface
water supply sources have variable raw water quality, this type of
operational flexibility is essential to successful development.

Surface Water: Availability and Yield Analysis

Surface Water Supply Facility Requirements

Treated Water ASR System
The ASR system consists of a wellfield into which excess treated water
is injected for ultimate withdrawal and distribution as needed.
Volumetrically, the ASR storage capacity is considered unlimited.
However, the hydraulic capacity of the ASR wellfield determines the
rate at which water can be injected and recovered. In general, the
required recovery rate will control the size of the ASR facilities.
For the purpose of the facility requirements simulation, ASR injection
or recovery capacity should not limit the reliability of the water supply
system. That is, sufficient ASR facilities will be constructed to
maximize the reliability of the water treatment plant, which is the
facilities component with the greatest cost. Therefore, ASR injection
capacity was set equal to treatment plant capacity, and ASR recovery
capacity was set equal to 1.5 times the potential yield for the
corresponding diversion capacity. By doing so, ASR capacity will not
limit the reliability of the simulated water supply systems.
Once treatment plant capacity and a corresponding net reliable yield
are determined after the simulation and treatment requirements
analysis, the required ASR capacity can be computed directly, based
on these values. The injection capacity will be equal to the maximum
amount available for injection, which is equal to the treatment plant
capacity minus the minimum monthly demand. On the other hand,
the maximum recovery rate is based on delivering the maximum
demand with the treatment plant shut down. Therefore, based on a
maximum day demand equal to 1.5 times the ADD, the ASR
withdrawal rate will also be equal to 1.5 times the ADD. In this way,
the ability to meet peak demands is fully satisfied by the ASR system.
The ability to meet long-term demands and fill the ASR storage area
must be met by upstream diversion and treatment components.

FACILITY REQUIREMENTS SIMULATION RESULTS
The simulation results indicate that reliable gross water supply yields
approaching the potential yield can be developed for most candidate
withdrawal sites. In general, the gross reliable yield is equal to about
95 percent of the potential yield. This is true for all sites except the
St. Johns River near Jacksonville, where adverse hydrologic
characteristics result in a gross reliable yield of only 72 to 78 percent of
the potential yield.

Surface Water: Availability and Yield Analysis

Surface Water Supply Facility Requirements

If there were not appreciable wastewater generated by the water
treatment process, then the gross reliable yield would equal the net
reliable yield. Net reliable yield, as used in this application, is the
water actually delivered to the distribution system, while gross reliable
yield is the water diverted from the stream and processed by the water
supply facilities. Gross reliable yield is identified by application of the
water supply systems simulation.
For conventional surface water treatment systems, volumetric losses
are generally in the range of 2 to 8 percent of the total raw water
inflow. The volume of wastewater generated will vary with the
characteristics of the sludge produced and the dewatering system
provided to treat the sludge. For the purpose of this preliminary
feasibility analysis, a loss of 5 percent is assumed. This means that the
volume of treated water produced by the conventional treatment
components is assumed to be equal to 95 percent of the total raw water
volume diverted for treatment.
For that portion of the diverted flow requiring desalting using RO
technology, volumetric losses can be more significant. The waste
residual, which is the concentrate produced in the desalting process,
ranges from about 15 percent of the flow treated by the RO component
to more than 50 percent, depending on the quality of the raw water.
Therefore, the gross reliable yield identified by application of the long-
term water supply systems simulation must be adjusted, based on
treatment requirements and raw water quality variability
considerations to establish net reliable yield. Thus, net reliable yield,
water quality characteristics, and treatability are interrelated.

WATER QUALITY AND TREATMENT REQUIREMENTS
Table 2 presents a summary of the water quality characteristics for
previously selected parameters for five USGS gauging stations of
interest to this investigation. The summary provided includes the
average, standard deviation, maximum value, minimum value, and
number of observations for each parameter for each gauge.
Each candidate withdrawal site corresponds directly to a gauging
station, with the exception of the St. Johns River at Sanford. The
St. Johns River near Titusville is the nearest upstream station to
Sanford and is considered to be most representative. Therefore, water
quality data for Titusville is also used to characterize expected water
quality at Sanford.

For this preliminary feasibility investigation, the available water quality
parameter of most concern is the chloride concentration reported in the
last column of Table 2. The magnitude and variability of the chloride
concentration will define in large part the degree of RO treatment
required. This, in turn, will impact the net reliable yield and,
eventually, the cost of developing the candidate water supply source.
The only truly fresh water source is Haines Creek. The maximum
observed chloride concentration is 40 milligrams per liter (mg/L), well
within the drinking water standard (DWS) of 250 mg/L. Development
of this site would require only conventional surface water treatment
consisting primarily of coagulation/sedimentation (clarification),
filtration, and disinfection using ozone and chloramines.
Periodically, all the St. Johns River candidate withdrawal sites exceed
the DWS for chlorides. Thus, each site would require desalting of at
least part of the flow for part of the time. In each case, a split-stream
treatment system is envisioned. In a split-stream treatment system,
only a portion of the total flow would receive RO treatment on an as-
needed basis. All flow would receive conventional treatment, similar
to that required for the Haines Creek source. When the inflow exceeds
90 percent of the DWS for chlorides (0.9*250=225), then a portion of the
inflow would also receive RO treatment so that the product water does
not exceed 225 mg/L. Product water is the treated water that actually
enters the distribution system and is delivered to the consumer.
As can be seen in Table 2, chloride concentration generally increases in
a downstream direction. Mean chloride concentration ranges from
127 mg/L near Cocoa to more than 3,500 mg/L above Jacksonville.
However, the water quality at De Land is slightly better and much less
variable than the water quality near Titusville, probably because of the
influence of the Wekiva River, which contributes significant high
quality flow between theses two stations. Because both Titusville and
Sanford are upstream of the Wekiva River, the Titusville data were
selected as most representative of conditions at Sanford.
Using the water quality summaries in Table 2, conceptual treatment
requirements for each candidate withdrawal site were established and
are reported in Table 3. All the sites will require conventional surface
water treatment, including chemical-aided sedimentation, filtration,
and disinfection. In addition, all of the St. Johns River candidate
withdrawal sites will require varying degrees of RO treatment. For the
purpose of this preliminary feasibility analysis, RO treatment is

Surface Water: Availability and Yield Analysis

Surface Water Supply Facility Requirements

Table 3. Major Water Treatment Processes Required for Each Candidate Surface Water
Withdrawal Site

aAll water treatment systems will require sludge thickening and dewatering facilities, finish water transfer pumping,
ground storage tankage, disinfection (ozone) and miscellaneous facilities including offices, and site work.
bDenotes required RO treatment capacity as a percentage of total conventional water treatment capacity
CDenotes required concentrate disposal capacity as a percentage of total conventional water treatment capacity

Surface Water: Availability and Yield Analysis

Surface Water Supply Facility Requirements

grouped into the following four major classifications, which are based
on maximum expected chloride concentration:
Slightly brackish. This classification applies when the maximum
chloride concentration is less than 500 mg/L. For this application,
the RO removal efficiency (salt rejection) is anticipated to be
90 percent and the concentrate volume is anticipated to be about
15 percent of the treated inflow.
Moderately brackish. This classification applies when the
maximum chloride concentration is greater than 500 mg/L, but less
than 1,000 mg/L. RO removal efficiency is expected to be about
90 percent and the concentrate volume will be about 20 percent of
the treated inflow.
Highly brackish. This classification applies when the maximum
chloride concentration is greater than 1,000 mg/L, but less than
5,000 mg/L. Expected RO removal efficiency is about 90 percent
and concentrate volume is about 30 percent of the treated inflow.
Saline. This classification applies when the maximum chloride
concentration is greater than 5,000 mg/L. The expected RO
removal efficiency is greater than 98.5 percent and the concentrate
volume is about 55 percent of the treated inflow.
These classifications are conceptual only; actual RO removal
efficiencies and concentrate volumes may vary considerably with
additional planning and preliminary design analysis. However, these
values are considered appropriate for the purpose of initial feasibility
evaluation and cost estimating.
As can be seen from Table 3, the St. Johns River near Cocoa is slightly
brackish. Most of the time, raw water will be well within the DWS for
chloride. However, the maximum chloride concentration of the
diverted flow is expected to be about 400 mg/L. Flow with the highest
chloride concentration (up to 570 mg/L) is associated with low river
flow and will not be diverted, based on the previously established
diversion rule. Therefore, under worst-case operating conditions, only
about 50 percent of the diverted flow would require desalting.
Under average or normal operating conditions, most flow would not
require desalting. Over the long-term, only about 2 to 3 percent of the
diverted flow would become waste concentrate, and the maximum
concentrated flow rate would equal approximately 7.5 percent of the

Surface Water: Availability and Yield Analysis

Surface Water Supply Facility Requirements

conventional treatment capacity. The net reliable yield is estimated to
be about 98 percent of the gross reliable yield.
The next three sites (Titusville, Sanford, and De Land) are similar.
Each is considered moderately brackish, with maximum raw water
chlorides greater than 500 mg/L, but less than 1,000 mg/L. The split-
stream treatment described previously for the Cocoa site would also
apply to these sites. The estimated required RO capacity ranges from
63 to 67 percent of the conventional treatment capacity and the
maximum concentrate flow would be on the order of 13 percent of the
total conventional treatment capacity. Net reliable water supply yield
for these three sites will be about 94 to 95 percent of the gross yield,
with only 5 to 6 percent of the diverted flow becoming waste
concentrate.
The final candidate withdrawal site, the St. Johns River near
Jacksonville, has poor water quality characteristics. Net outflow at this
point can be relatively good quality fresh water, or it can be sea water
or a mixture of the two. Chlorides have ranged from 71 mg/L to
11,000 mg/L. Chloride concentrations can also be high at any flow
rate. Sea water will flow upstream during incoming tides and be part
of the outflow on the outgoing tide. The Jacksonville site is considered
saline, because the diverted raw water will often exceed 5,000 mg/1
chlorides, and would require construction of sea water RO facilities.
Over the long term the reliable net yield would be about 65 percent of
the reliable gross yield. That is, about 35 percent of the total diverted
flow would become waste concentrate.
Given the very poor hydrologic and water quality characteristics of
this site and the expensive and relatively under-used facilities required
to develop the potential water supply, this site is not considered a
feasible surface water supply alternative and should not be evaluated
in future phases of the SJRWMD alternative water supply
investigations.
These adverse hydraulic and water quality conditions apply only to
the downstream portion of the main stem of the St. Johns River. It is
possible that tributaries to the lower St. Johns River could be
developed as viable water supply sources if the withdrawal sites are
located above tidal influence or behind constructed salinity barriers.
Candidate watersheds may include Black Creek in Clay County or
Deep Creek in St. Johns County. Evaluation of these hydrologic
systems would be hampered, however, by a lack of basic long-term
streamflow and water quality data.

Surface Water: Availability and Yield Analysis

Surface Water Supply Facility Requirements

RELIABLE NET YIELD AND FACILITY REQUIREMENTS
The results of the long-term systems simulation and the water quality
and treatment requirements analysis were used to establish estimates
of the reliable net yield for each of the trial water supply systems. The
reliable yield, along with the facility capacities required to develop that
yield, are reported in Table 4.
There are six reliable yield estimates and six water supply systems
defined for each of the candidate water withdrawal sites. For example,
at the Lake Griffin site, reliable yields of up to 28 mgd could be
developed. Facilities required to develop the maximum 28-mgd yield
include a 40-mgd water diversion structure, a 38-mgd conventional
water treatment plant, and a 42-mgd ASR system. An off-line raw
water reservoir with a 200-million-gallon (MG) capacity would also be
needed. This water supply system will fully meet the desired monthly
demand at least 98.3 percent of the time.
As previously discussed, the planned minimum flow and levels analysis
for Lake Griffin may further restrict the reliable net yield available from
this candidate withdrawal point. Therefore, to provide a relatively
conservative estimate of Lake Griffin water supply potential, the
maximum net reliable yield to be evaluated in the University of Florida
decision model will be limited to 50 percent of the maximum net reliable
yield estimated in this analysis, or 14 mgd (0.5 x 28).
If Lake Griffin appears to be a desirable water supply source, as determined
by application of the University of Florida decision model, then it may be
necessary to re-evaluate Lake Griffin facility requirements and costs. This
re-evaluation would be based on a new diversion rule established after the
planned minimum flows and levels analysis is complete.
The St. Johns River sites would require additional facilities. The
maximum reliable net yield for the St. Johns River at Sanford is about
279 mgd. To fully develop this yield, substantial facilities would be
required including a 392-mgd river diversion structure, a 2-billion-
gallon off-line storage reservoir, a 372-mgd conventional water
treatment plant, a 223-mgd RO treatment facility, a 419-mgd ASR
system, and a 45-mgd concentrate disposal system.
The data reported in Table 4 can be used to estimate the approximate
facility requirements for any desired yield at any of the candidate
withdrawal sites by linear interpolation. Figures 22 through 27
illustrate the relationship between net reliable yield and required
facilities for each of the six candidate withdrawal sites.

The surface water supply cost estimates will include development of a
complete array of planning-level cost estimates for six different size
facilities at five different candidate withdrawal sites. Cost functions
for each withdrawal site (net reliable yield [ADD] vs. cost) will also be
developed and a TM will be produced to report the methods used and
results obtained.

SITES CONSIDERED
All candidate surface water withdrawal sites, with the exception of the
St. Johns River above Jacksonville, will be included in the cost
estimating phase of the investigation. As discussed previously, the
Jacksonville site does not provide a practical alternative for municipal
water supply development.

COST PARAMETERS AND CRITERIA
Cost parameters to be considered have been previously established by
the project team and include the following:
Construction cost
Non-construction capital cost
Land cost
Land acquisition cost
Total capital cost
Operation and maintenance (O&M)
Equivalent annual cost
Annualized set-up cost
Annualized unit cost
Economic criteria, including cost basis, non-construction capital cost
factor unit land costs, interest rate, and facilities life expectancies, have
been previously established for all cost estimates developed as part of
the SJRWMD alternative water supply strategies investigations. These
previously established criteria will be used to develop the required
cost estimates for the surface water facilities.

Surface Water: Availability and Yield Analysis

Proposed Cost Estimation Procedure

CONSTRUCTION AND O&M COST COMPONENTS

Construction and O&M cost estimates will be developed at the
preliminary planning or cost curve level for the major components
required. Major components required for each candidate withdrawal
site may include the following:

ASR system
wells
pumps
piping and I&C
Applicable cost curves will be identified in the literature. Where
necessary, cost curves or unit costs for individual items (e.g., filtration)
or major systems (e.g., conventional surface water treatment) will be
developed. Using the identified or developed construction and O&M

Surface Water: Availability and Yield Analysis

Proposed Cost Estimation Procedure

cost curves, a spreadsheet application will be developed. This
spreadsheet will be used to develop the required cost estimates for six
different water supply yields at the five candidate withdrawal sites.
The facility capacities to be used in the cost estimating procedure are
presented in Table 4, parts a through e.

LAND COSTS
Land requirements will be estimated for the off-line raw water storage
reservoir, the water treatment plant, and ASR wellfield. Total land
costs, including the cost of acquisition, will then be estimated, based on
the estimated total land requirement for each of the 30 facilities
considered.

OTHER COST ESTIMATES
Other cost parameters, including total capital cost, equivalent annual
cost, set-up cost, and unit cost, will be estimated, based on the
construction, land, and O&M costs computed for each facility. These
cost estimates will be included in the cost estimating spreadsheet and
will be developed in accordance with the cost estimating guidelines
and economic criteria established for the SJRWMD alternative water
supply investigations.

COST FUNCTIONS
The cost analysis will result in the development of estimated costs for
each of the eight cost parameters for six different water supply systems
at each of the five candidate water supply withdrawal sites. These
individual cost estimates will be used to develop cost equations for
each cost parameter applicable to the individual withdrawal sites. The
resulting cost equation will likely have the following general form:
COST(p,1) = a(p,) + b(p,) RNY c(p,l)
Where:
COST(p,1) = estimated cost of parameter p, at withdrawal site location
1, in total dollars or dollars per year, depending on the units of the cost
parameter.
RNY = reliable net water supply yield in mgd. This is also the ADD
delivered to distribution.

Surface Water: Availability and Yield Analysis

Proposed Cost Estimation Procedure

a(p,j) b(p,l) and c(p,l) are best fit parameters for each equation as
determined by regression analysis.
To provide added flexibility, the costs associated with the off-line raw
water reservoir will be considered separately from the other water
supply system components, including the river diversion structure, the
water treatment plant, and the ASR system. Surface water supply
system costs with and without the reservoir component may then be
evaluated if desired.
These equations may be used to estimate any cost parameter for any
desired water supply yield, within the range investigated, for each
candidate withdrawal site. These equations will be used in the
University of Florida Decision Model to define the cost characteristics
of the surface water supply alternative.

TECHNICAL MEMORANDUM
A TM reporting the methods and results of the surface water supply
cost estimating and cost equation development will be prepared.

Surface Water: Availability and Yield Analysis

Summary and Recommendations

SUMMARY AND RECOMMENDATIONS

SUMMARY
This preliminary surface water availability and yield analysis
addresses the municipal water supply development potential of six
previously selected candidate surface water supply withdrawal sites
(CH2M HILL, 1996b). The locations of the six sites are as follows:
Lake Griffin (Haines Creek)
St. Johns River near Cocoa
St. Johns River near Titusville
St. Johns River at Sanford(Lake Monroe)
St. Johns River near De Land
St. Johns River above Jacksonville
In evaluating these sites, similar analyses were conducted that
included the following elements:
Development of flow duration curves
Determination of minimum streamflow requirements and
maximum water supply withdrawal rate
Evaluation of the effect of water supply withdrawal on the flow
duration relationship
Evaluation of the potential water supply yield as a function of
maximum installed withdrawal capacity
Determination of streamflow water quality characteristics and
water treatment requirements
Estimation of the type and size of water supply facilities required
as a function of the total reliable water supply yield developed
Flow Duration Analysis
There were two primary objectives for the streamflow duration
analysis. First, the flow duration curves for each candidate withdrawal
site were established to determine the frequency of allowable water
supply diversion, the minimum streamflow requirements, and the
maximum diversion rate to be investigated.

Surface Water: Availability and Yield Analysis

Summary and Recommendations

For this project, minimum streamflow requirements are defined as the
positive streamflow rate observed 95 percent of the time. Using this
rate, at least 5 percent of the time (during low-flow periods) water
supply withdrawal will not be allowed. In addition, the maximum
withdrawal rate considered is equal to 25 percent of the long- term
average flow rate. Lesser withdrawal rates are also considered.
These minimum streamflow and maximum diversion rate criteria, as
well as the source evaluation methodologies in this TM, were
previously established for the purpose of this preliminary feasibility
analysis (CH2M HILL, 1996a). If these criteria change, then all facility
requirements reported in this TM will also change. This is because
surface water facility requirements are a direct function of the allowed
diversion criteria; thus, the results reported in this TM are valid only
for the previously selected diversion criteria.
Once the withdrawal parameters were established, the maximum
effect on the flow duration relationship for each candidate withdrawal
site was investigated. From this effort, it was determined that there
are little noticeable effects if the entire streamflow regime is
considered. However, if only the normal and low-flow portions of the
streamflow regime are considered, the water supply withdrawal
effects are more apparent. The water supply withdrawal tends to
flatten the flow duration curve at moderate flow rates. At flow rates
less than the minimum withdrawal rate, the flow duration relationship
would be unchanged because water supply diversion would not be
allowed.
Potential Yield Analysis
The objective of the potential yield analysis is to establish a
relationship between the installed river diversion capacity and the
maximum long-term volume of water that may be withdrawn for
water supply. This parameter is termed potential yield because it
represents the maximum possible water supply yield, if sufficient
storage and treatment facilities are constructed to fully use the
diverted flow and assuming there is no waste in the treatment process.
The maximum potential yield for the Lake Griffin site is approximately
75 percent of the maximum diversion capacity. For the four upstream
St. Johns River sites (Cocoa to De Land), the maximum potential yield
ranges from 81 to 84 percent of the installed maximum diversion
capacity. For the downstream St. Johns River site (above Jacksonville),

Surface Water: Availability and Yield Analysis

Summary and Recommendations

the maximum potential yield is only 64 percent of the maximum
installed diversion capacity.
Surface Water Supply Facility Requirements
Facilities required to develop the surface water supply at each
candidate withdrawal site were determined by a combination of
facilities simulation and water quality and treatability analyses. In
each case, required facilities included the following:
River diversion structure
Off-line raw water storage reservoir
Water treatment plant
ASR system
The simulation analysis estimates the gross reliable yield, which could
be developed for each site for a selected array of facility sizes. The
water quality and treatability analysis established the treatment
processes needed in the water treatment plant component of the water
supply system. Also, the analysis provides a preliminary quantitative
estimate of the wastewater volume produced. These volumetric losses
include losses associated with conventional surface water treatment, as
well as the waste concentrate produced by the required desalting. The
total volumetric loss must be subtracted from the system gross yield to
obtain the net reliable yield, which is the final estimate required. The
net reliable yield is defined as the average daily demand that can be
reliably delivered to the distribution system by the surface water
supply facilities.
The results of the water availability and yield analysis are summarized
in Table 5. Lake Griffin is the only true freshwater site among the
candidate withdrawal sites considered. Desalting will not be required
at this site and a waste concentrate stream will not be produced.
Therefore, the estimated maximum reliable yield for the Lake Griffin
withdrawal site, 28 mgd, is nearly equal to the maximum potential
yield of 30 mgd.
The planned SJRWMD minimum flow and levels analysis for Lake
Griffin may further restrict the reliable net yield. Therefore, to provide
a relatively conservative estimate of Lake Griffin water supply
potential, the maximum net reliable yield, to be evaluated by the
University of Florida decision model, will be limited to 50 percent of
the maximum net reliable yield estimate in this analysis, or 14 mgd
(0.5 x 28).

Note: The maximum yield values for the St. Johns River sites are not independent. These values represent
cumulative amounts for the candidate withdrawal site and all upstream sites. For example if a 100-mgd reliable
water supply were developed near Titusville the maximum reliable yield at De Land would be reduced by 100 mgd
from 351 mgd to 251 mgd.
aMaximum reliable yield for Lake Griffin considered in the University of Florida decision model will be limited to
70 percent of this value or 19.6 mgd.

Surface Water: Availability and Yield Analysis

Summary and Recommendations

The four upstream St. Johns River candidate withdrawal sites (Cocoa
to De Land) are similar to each other. The worst-case water quality
diverted for use at these sites is classified as either slightly or
moderately brackish. Under many flow conditions, desalting will not
be required. However, some desalting would be required for some of
the diverted flow. Also, a waste concentrate would be produced,
reducing the net reliable yield to about 108 mgd to 351 mgd, or about
85 percent of the maximum potential yield. Concentrate volume
would be on the order of 5 percent of the total diverted flow.
The final candidate withdrawal site, the St. Johns River above
Jacksonville, has poor water quality characteristics because of
significant tidal mixing. The worst-case water quality at this site is
saline or near seawater conditions, with observed chloride
concentrations of more than 10,000 mg/L. This water would require
extensive desalting, generating a large amount of concentrate. The
estimated maximum reliable yield that could be developed at this
location is only 44 percent of the maximum potential yield. About
35 percent of the diverted flow would become waste concentrate.
These adverse hydraulic and water quality conditions apply only to
the downstream portion of the main stem of the St. Johns River. It is
possible that tributaries to the lower St. Johns River could be
developed as viable water supply sources if the withdrawal sites are
located above tidal influence or behind constructed salinity barriers.
Candidate watersheds may include Black Creek in Clay County or
Deep Creek in St. Johns County. Evaluation of these hydrologic
systems would be hampered, however, by a lack of basic long-term
streamflow and water quality data.

RECOMMENDATIONS
It is recommended that five of the six candidate surface water
withdrawal sites be considered further in the cost estimating phase of
these investigations. These sites are as follows:
Lake Griffin (Haines Creek)
St. Johns River near Cocoa
St. Johns River near Titusville
St. Johns River at Sanford(Lake Monroe)
St. Johns River near De Land

Surface Water: Availability and Yield Analysis

Summary and Recommendations

Because of its poor hydrologic and water quality characteristics, the
sixth candidate withdrawal site, the St. Johns River above Jacksonville,
should not be considered further. The results of this analysis indicate
that this site is not a viable municipal surface water supply source.
Thus, it is unlikely that this site would prove to be an economically
viable municipal water supply source under any foreseeable set of
withdrawal criteria or other operating conditions.

The cost estimating procedure recommended in this TM should be
approved and applied to the five remaining candidate withdrawal
sites.